Line-of-sight detection techniques for detecting the direction of the line of sight and the position of the gaze of a user are known. An example of a line-of-sight detection method is a method in which a corneal reflection of a light source and a pupil are detected from an image obtained by capturing an image of an eye of a user and the line of sight of the user is detected based on the positional relationship between the corneal reflection and the center of the pupil.
It is demanded that the position of the corneal reflection and the position of the center of the pupil be accurately detected in this method. However, when the distance between the illuminating light source and the camera is small, light from the illuminating light source is reflected by the retina and this reflected light reaches the camera via the pupil. Consequently, the occurrence of a bright pupil state is known in which the entire pupil is bright in the image captured by the camera. In the case where a bright pupil state exists, the outline of the corneal reflection may become indistinct and it may be difficult to detect the corneal reflection.
In response to this problem, a technique has been proposed in which the distance from the camera to the face of the user is estimated, it is determined whether a bright pupil state exists based on a ratio of the estimated value of the distance to the distance between the illuminating light source and the camera and the line-of-sight detection method to be used is switched in accordance with the result of this determination (For example, Japanese Laid-open Patent Publication No. 2014-67102).